Means of improving data transfer

ABSTRACT

A process for cooperative aerial inter-antenna beamforming for communication between (a) multiple moving platforms, each platform having an aerial antenna mounted thereon, such that the aerial antennas have variable positions and orientation over time, and (b) at least two ground based antennas; the process involving transmitting data relating to the positions of the aerial antennas to a processing system, the processing system calculating and transmitting beamforming instructions to the ground based antennas, the ground based antennas thereby transmitting or receiving respective component signals for each aerial antenna, the component signals for each aerial antenna received or transmitted by the ground based antennas having essentially the same information content but differing in their phase and usually amplitude, so as to form a cooperative beam from the cooperative sum of the signals between the ground based antennas and the at least two aerial antennas.

TECHNICAL FIELD

The invention relates to means of improving backhaul data transfer toand from aerial antennas involved in cooperative beamforming. These arefirstly, inter-antenna beamforming from ground based or low altitudeantennas with high altitude antennas utilizing multiple phase-arrayantennas, secondly, the use of polarization information on such beams toand from ground based antennas, and thirdly, the use of free spaceoptical systems or lasers to improve the delivery of precisioninformation services, including telecommunications, earth observation,astronomical and positioning services.

BACKGROUND TO THE INVENTION

High altitude platforms (aircraft and lighter than air structuressituated from 10 to 35 km altitude)—HAPS, have been proposed to supporta wide variety of applications. Areas of growing interest are fortelecommunications, positioning, observation and other informationservices, and specifically the provision of high speed Internet, e-mail,telephony, televisual services, games, video on demand, and globalpositioning.

High altitude platforms possess several advantages over satellites as aresult of operating much closer to the earth's surface, at typicallyaround 20 km altitude. Geostationary satellites are situated in around40,000 km altitude, and low earth orbit satellites are usually at around600 km to 3000 km altitude. Satellites exist at lower altitudes buttheir lifetime is very limited with consequent economic impact.

The relative nearness of high altitude platforms compared to satellitesresults in a much shorter time for signals to be transmitted from asource and for a reply to be received (which has an impact on the“latency” of the system. Moreover, high altitude platforms are withinthe transmission range for standard mobile phones for signal power andsignal latency. Any satellite is out of range for normal terrestrialmobile phones operating without especially large or specialist antennas.

High altitude platforms also avoid the rocket propelled launches neededfor satellites, with their high acceleration and vibration, as well ashigh launch failure rates with attendant impact on satellite cost.

Payloads on high altitude platforms can be recovered easily and atmodest cost compared to satellite payloads. Shorter development timesand lower costs result from less demanding testing requirements.

U.S. Pat. No. 7,046,934 discloses a high altitude balloon for deliveringinformation services in conjunction with a satellite.

US 20040118969 A1, WO 2005084156 A2,U.S. Pat. No. 5,518,205 A, US2014/0252156 A1, disclose particular designs of high altitude aircraft.

However, there are numerous and significant technical challenges toproviding reliable information services from high altitude platforms.Reliability, coverage and data capacity per unit ground area arecritical performance criteria for mobile phone, device communicationsystems, earth observation and positioning services.

Government regulators usually define the frequencies and bandwidth foruse by systems transmitting electromagnetic radiation. The shorter thewavelength, the greater the data rates possible for a given fractionalbandwidth, but the greater the attenuation through obstructions such asrain or walls, and the more limited diffraction which can be used toprovide good coverage. These constraints result in the choice of carrierfrequencies of between 0.7 and 5 GHz in most parts of the world withtypically a 10 to 200 MHz bandwidth.

There is a demand for high data rates per unit ground area, which israpidly increasing from the current levels of the order 1-10 Mbps/squarekilometre.

To provide high data rates per unit ground area, high altitude unmannedlong endurance (HALE) aircraft, or free-flying or tethered aerostats,need to carry large antenna(s) to distinguish between closely basedtransceivers on the ground. A larger diameter antenna leads to a smallerangular resolution of the system, hence the shorter the distance on theground that the system can resolve. Ultimately the resolution isdetermined by the “Rayleigh criterion” well known to those skilled inthe art. The greater the antenna resolution, the higher the potentialdata rates per unit ground area there are.

However fitting extremely large diameter antenna or antennas of 50metres or more onto platforms is not feasible with current or envisagedaircraft technology.

Phased array digital “beamforming” (DBF) and multi beam horn (MBH)antennas have been considered for high altitude platforms in forexample, R. Miura and M. Suzuki, “Preliminary Flight Test Program onTelecom and Broadcasting Using High Altitude Platform Stations,”Wireless Pers. Commun., An Int'l. J., Kluwer Academic Publishers, vol.24, no. 2, January 2003, pp. 341-61. Other references include:http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=620534,http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=933305,http://digital-library.theiet.org/content/journals/10.1049/ecej_20010304,http://digital-library.theiet.org/content/journals/10.1049/el_20001316http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=4275149&pageNumber%3D129861However, the prior art suggest that use of high altitude platforms doesnot represent a promising way forward to delivering next generationcommunication means.

SUMMARY OF THE INVENTION

In a first aspect, the invention relates to a process for cooperativeaerial inter-antenna beamforming for communication between (a) multiplemoving platforms, each platform having an aerial antenna mountedthereon, such that the aerial antennas have variable positions andorientations over time, and (b) at least two ground based antennas; theprocess involving transmitting data relating to the positions of theaerial antennas to a processing system, the processing systemcalculating and transmitting beamforming instructions to the groundbased antennas, the ground based antennas thereby transmitting orreceiving respective component signals for the at least two aerialantennas, the component signals received or transmitted by the groundbased antennas having essentially the same information content butdiffering in their phase and usually amplitude, so as to form acooperative beam from the cooperative sum of the signals between theground based antennas and the aerial antennas.

Additionally, the invention relates to a process for cooperative aerialinter-antenna beamforming for communication between at least two aerialantennas, mounted on at least one moving platform, such that the atleast two aerial antennas have variable positions and orientation overtime, and at least two ground based antennas; the process involvingtransmitting data relating to the positions of the at least two aerialantennas to a data processing system, a processing system calculatingand transmitting beamforming instructions to the ground based antennas,the ground based antennas thereby transmitting or receiving respectivecomponent signals for each aerial antenna, the component signals foreach aerial antenna received or transmitted by the ground based antennashaving essentially the same information content but differing in theirphase and usually amplitude, so as to form a cooperative beam from thecooperative sum of the signals between the ground based antennas and theat least two aerial antennas, the resulting cooperative beam therebyhaving the same or similar properties of a beam formed from a notionalsingle ground based antenna large enough to encompass the positions ofthe at least two ground based antennas.

By the term “same or similar” is meant properties such as beam size.

In a second aspect, the invention relates to apparatus for providing acommunication network, for communication between (a) multiple movingplatforms, each platform having an aerial antenna mounted thereon, suchthat the aerial antennas have a variable position and orientation overtime, and (b) at least two ground based antennas; the network involvinga data processing system that calculates and transmits beamforminginstructions to the ground based antennas, the ground based antennasthat transmit or receive respective component signals for each aerialantenna, the component signals for each aerial antenna havingessentially the same information content but differing in their phaseand usually amplitude, thereby forming a cooperative beam from thecooperative sum of the signals between the ground based antennas and theaerial antennas.

Additionally, the invention relates to apparatus for providing acommunication network, for communication between at least two aerialantennas, mounted on at least one moving platform, such that the atleast two aerial antennas have a variable position and orientation overtime, and at least two ground based antennas; the network involving adata processing system that calculates and transmits beamforminginstructions to the ground based antennas, the ground based antennasthat transmit or receive respective component signals for each aerialantenna, the component signals for each aerial antenna havingessentially the same information content but differing in their phaseand usually amplitude, thereby forming a cooperative beam from thecooperative sum of the signals between the ground based antennas and theat least two aerial antennas, the resulting cooperative beam therebyhaving the same or similar properties of a beam formed from a notionalsingle ground based antenna large enough to encompass the positions ofthe at least two ground based antennas.

Synthetic aperture synthesis has long been known in radio astronomywhere the resolution of a large antenna is synthesized by using thesignals from appropriately spaced relatively small antennas. IndeedMartin Ryle and Antony Hewish shared the Nobel prize for physics in 1974for this and other contributions to the development and use of radiointerferometry. Related technology to aperture synthesis has been usedfor many years in low frequency radio communication to submarines, inacoustics, phased arrays in LTE and WiFi systems. However its use forcommunication to and from ground based or aerial user equipment hasnever been previously considered.

Thus, through application of aperture synthesis principles a cooperativebeam can be formed that has a narrow width as could be provided by anotional single antenna large enough to encompass the positions of theat least two ground based antennas. As would be known to a personskilled in the art, the larger the notional antenna, the narrower thebeam.

Building on techniques developed for the quite remote technical field ofradio astronomy it has been discovered that generation of these verynarrow cooperative beams can be achieved by altering the phasing andweighting of the various signals sent to or received from each groundbased antenna.

The invention exploits the ability of suitable measurement systems todetermine the relative position of the ground based antennas, to withina fraction of a wavelength of the electromagnetic radiation being used,even up to GHz frequencies. As described above, with appropriate signalprocessing to enable “aperture synthesis,” similar to that commonly usedin radio astronomy, it is then possible to obtain a beam resolutioncomparable to that of a ground based antenna with a diameter equal to asignificant fraction of the maximum separation distance of the groundbased antennas. To achieve such aperture synthesis, an antenna'sposition relative to all the other antennas is preferably determined towithin approximately ⅙ of a wavelength, preferably 1/10 of a wavelength,and this has become possible with modern positioning techniques to theaccuracy required for the operation of phased arrays for mobilecommunications.

A key feature of the invention is that three or more ground basedantennas in communication with the aerial antennas provides co-operativeinter-antenna beam-forming for very targeted communications withindividual aerial antennas: the beam used for a single aerial antenna isvery small, such that other aerial antennas nearby, within a few tens ofmetres or less, can also receive or transmit a full bandwidth signal—onthe same carrier frequency.

The invention enables an increased use of backhaul bandwidth and therebya reduced number of ground-based antennas for a given data transferrate, where the relative position of the ground based or low altitudeantennas is known to within better than a quarter of the wavelength usedfor data transmission and the aerial antennas are so close together thatthey could not be resolved from one another by the individual groundbased antennas.

Backhaul ground stations (BG stations), support the high-speed datalinks between the aircraft and a system-processing centre.

The benefit of the invention is that the number of BG stations and theirassociated costs, which can be significant in respect of the overallcosts of the communication system, can be reduced if the BG stationshave multi-beaming capability so that they can communicate with eachplatform independently when there is a fleet of platforms in line ofsight.

The benefits of the invention increase where inter-aerial antenna beamforming is utilized to allow more effective use of spectrum and/orbetter beam focusing with UE and a large number—at least 3 but oftentwenty or more platforms are necessary to carry the aerialantennas—depending on UE data requirements.

In a preferred embodiment of the invention, separated polarizationinformation for the beams communicating to and from aerial antennas canbe used to increase the rate of data transfer per BG station.

This involves the use of the two orthogonal polarisations of thetransmit and receive beams for backhaul communications between theground stations and the aerial antennas to provide two separate datastreams which increases the data transfer rate on the backhaul links byup to double that of a conventional link. This also reduces the numberof ground stations required.

The invention will now be illustrated by way of example particularlywith reference to an implementation referred to as “HAP-CELL”, whichutilises cooperative aerial antenna beamforming, and with reference tothe following figures in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system according to theinvention.

FIG. 2 is an illustration of a phased array.

FIG. 3 illustrates beam forming on a single phased array.

FIG. 4 illustrates beam formation by a constellation of antennassupported by aircraft.

FIG. 5 is a schematic representation of the system arrangement andconnection with a mobile telecommunications network.

FIG. 6 is a schematic arrangement of an aircraft communication system.

FIG. 7 is a schematic arrangement of a backhaul ground based station (BGStation) system.

FIG. 8 illustrates multiple HAP-Cell systems.

FIG. 9 illustrates multiple platforms supported by tethered aerostats.

FIG. 10 illustrates an example of how beams from one or more aerialantenna(s) can be modified to give good coverage up to a nationalboundary but minimize energy spillover.

FIG. 11 illustrates backhaul utilizing free space optics.

DESCRIPTION

A glossary of terms is described in Table 3.

The HAP-CELL system supported by the invention can provide high datarate communications to and from UE with an interface to a conventionalmobile telecommunications network or Internet.

The HAP-CELL system allows for the support of standard interfacespecifications and protocols or proprietary interface protocols. In theillustrative example, there is support for communications with standard,unmodified mobile phones, smartphones, tablets or mobile computers asthe UEs. Other user devices that could be supported would betransceivers on vehicles, vessels or aircraft, or fixed devices on orinside buildings to enable the connection of electronic devices to theInternet.

The HAP-CELL system is furthermore capable of connecting to thepre-existing mobile phone network and Internet through appropriateinterfaces. The communications topology can be arranged in the samefashion as a conventional mobile phone network, and in that case, thepresent invention can be used as part of a conventional mobile network.

FIG. 1 is a schematic representation of the system. FIG. 1 illustratesjust one potential configuration: utilizing multiple aircraft (8) as theplatforms to create the constellation of antennas over e.g.approximately a 60 km diameter “Service area” (13).

The system uses a “constellation” of antennas mounted on multipleplatforms (9) operating at approximately 20 km altitude. These platformscan be aerostats, tethered or free flying; or manned or unmannedaircraft. In the case of aircraft, they can be solar powered for longendurance at suitable latitudes and seasons, or use hydrogen as a highenergy density fuel for applications that require higher-poweredequipment or in areas that have limited solar irradiation at particularseasons. Other fuels such as hydrocarbons can be utilized.

In FIG. 1, each aircraft platform (9) supports two antennas (15,16), oneused for transmission and one for reception. In one embodiment, theplatforms carry phased array systems, or horn antenna systems. Thesesystems, when using beamforming technology, can provide many separatebeams (6,7) in different directions to communicate with UEs (11)situated on different “patches” (10), areas illuminated by an antennabeam, and can also provide the “backhaul” links (5) to the “backhaulground”, BG stations (4).

The invention can provide communication links with BG stations (4) toprovide the backhaul data communication systems that support the UEactivities with the rest of the cellular network. The BG stations canalso use phased array systems with beamforming technology to communicatedirectly with the platforms under the control of a computer processingsystem, e.g. a ground-based computer processing centre, or simpler dishor horn-based systems. The BG stations can be connected to theground-based computer processing centres (1) via standard protocols; byfibre optic, or microwave connections or any other physical connectiontechnology (3). For simplicity not all the links to the backhaulstations are shown in FIG. 1.

An illustrative embodiment of the system, as shown in FIG. 5 includes:

-   -   1. The platform based phased array antennas, which communicate        with the UE (UE₁, UE₂ to UE_(n)) and BG stations (51,52)        supported by aerial platforms (not shown).    -   2. Optional additional platform based receivers and transmitters        that carry the backhaul data links (not shown).    -   3. The BG stations or other antennas which communicate with the        platforms and link to the processing centre.    -   4. A processing centre (53), which calculates all the parameters        for the communication links and provides the interface to the        wider cellular network. (54).

Thus, the system provides that a constellation of antennas (normally atleast three, but typically fifteen or even many hundred in line of sightwithin the area in which the ground based UE resides) provideco-operative or inter-platform beamforming for very targetedcommunications with individual users, see FIG. 1: the beam (12) used fora single user within a particular patch is very small.

Utilizing the system a targeted beam may be formed on a single UE: theintersection of this with the ground can be presented to the mobilenetwork as an individual cell which has the ability to use the fullavailable resources (signal bandwidth and communication power) forcommunication to a single piece of UE. These cells are termed herein as“dynamic femtocells” or DF-Cells.

Laser Communication and Free Space Optics

In certain locations where the availability of BG stations is low, itmay be advantageous to link one aircraft with another more suitablylocated over BG stations by laser or free space optical devices. Thesehave been developed in recent years and allow high data ratecommunication (greater than 1 Giga bit per second) with modest (under100 W) power consumption and can be of modest weight of less than 25 kgbut able to communicate in the stratosphere at distances of at least 60km, and more preferably of 250 km and on occasion of 500 km or more.With such an arrangement it is possible for one or more aerial antennasto be linked to BG stations many hundreds if not thousands of kilometersdistant by utilizing laser links between additional aircraft.

Thus, in a preferred embodiment, the invention relates to the use oflasers or free space optical devices to provide a communication linkbetween aerial antennas involved in cooperative inter antennabeamforming.

The use of lasers and free space optics for high altitude aircraft iswell known to those skilled in the art as shown for example inhttp://www.vialight.de

This is illustrated in FIG. 11, which shows beam formation and backhaularrangements in the service area, by antennas on fleets of platformslabelled F₁, F₂ to F_(m). The antenna on F₁ is shown producing twocollections of beams (180, and 182), which are directed at two areas(181, and 183). F₂ to F_(m) are in line of sight of BG stations in area185 and communicate directly with them.

However the antennas on platforms in fleet F₁ are not in line of sightof any BG stations so backhaul to and from BG stations is passed bylaser communications (184) to an intermediate high altitude platformHAPI₁, which in turn communicates (186) to a second intermediate highaltitude platform HAPI₂, which then is in communication with BG groundstations in patch 185.

HAPI₂ could also be a high altitude platform on a tethered aerostat andbe directly linked to the ground via an optical fibre.

The use of Free Space Optical devices or lasers to communicate betweenaerial antennas is used to promote data transfer from areas where thereare limited or no ground based communication links, for example overlarge areas of water, desert or undeveloped land to aerial antennaswhich can be situated where there are suitable ground based links whichcan be reached by microwave transmission to and from the aerialantennas.

With high altitude aircraft high aspect ratio wings are necessary toprovide the low drag needed for such aircraft to have sufficientendurance to allow sustained station holding—weeks rather than days.Aspect ratios of at least 20:1, preferably 30:1 are needed. These longwings can easily interrupt, with very modest yaw, or roll, almosthorizontal—within 5 degrees of the horizontal—laser transmissions whichare required for long distance—over 100 km—communication betweenaircraft platforms. To avoid this it has been discovered that a suitablecontrol system is needed which identifies the direction and alignment ofcommunication laser beams in operation and interfaces with the aircraftattitude control system to ensure that the plane attitude avoidsinterruption of the laser beams by angled wings or winglets.

When such lasers or free space optics are employed it has beendiscovered that a sophisticated control system is required for the highaltitude platforms to ensure that the attitude of the aircraft does notbring wings or wing-tips to obstruct the laser beam(s) used forcommunication. In normal aircraft communications by lasers, thecommunication is downwards or by aircraft with relatively small wingspans and so with suitable siting of the laser transmitters andreceivers it is relatively easy to maintain un-obscured communication.

For the case of autonomous high aircraft engaged in cooperative interantenna beam forming, the direction of the laser beams and the positionof the aircraft needs to modify the autonomous system outputs to ensureby changing pitch, yaw and roll, as well as flight path, thatuninterrupted communication is permitted.

The communication of particular data, applications and content may havedeleterious effects on user equipment or particular users, for example,children. The present system allows a system operator to introducechecks in the processing centre or elsewhere on data, applications andcontent to protect user equipment or particular users.

Thus, in a further aspect the invention relates to a method of receivingand/or transmitting data, applications and/or content to an antenna onuser equipment, the method utilising the network or process as describedherein.

The present system allows for much more precise identification ofgeographic location within a wide area coverage, along with higher datarates, than current systems.

Currently in macrocells outside urban areas other than by using anadditional system such as differential GNSS e.g., GPS, GLONAS andGALILEO, locations are difficult to establish to less than tens if nothundreds of metres. Even within urban areas with microcells locations of10 m or less are difficult to obtain.

Within a large area accessible by a constellation of antennas, locationcan often be identified within metres and even to sub-metre resolution,dependent on propagation conditions. This allows the system at theresolution of rooms or buildings the capability to restrict access tospecific or general user equipment on a continuous or intermittentbasis.

Such an access capability has the potential to allow appropriateauthorities within properties over which they have suitable rights torestrict or modify access, for example to control under age or visitoraccess in specific rooms, at specific times or continuously. Thiscapability also has the ability to readily provide information on thelocation of the user equipment to another party contacting another pieceof user equipment.

Thus, in a further aspect, the invention relates to a process for themanagement of access to the process described herein by specifying thelocation and/or time that will permit the transmission or reception ofinformation to that location.

Phased Array Antennas and Inter-Antenna Beamforming Technology

The UE may include transmitters or receivers or both. The ground-basedand aerial antennas can be phased arrays or conventional antennas orboth.

As discussed above, the HAP-CELL system involves the use of advancedphased arrays, which enable “intra-array beamforming” or beamformingwithin a single antenna. There follows a brief description of thesetechnologies.

Phased arrays consist of a large number of individual antenna elements,but in the rest of this document “antenna(s)” will refer to one or morephased arrays or one or more conventional individual antenna(s) such asa horn antenna(s).

Phased arrays have a particular advantage for high altitude aircraft andother platforms in that their aspect ratio, the ratio of their width todepth is generally low, and thereby often easier to mount in a structurewhere low aerodynamic drag is required.

Antenna(s) mounted on high altitude platforms can communicate both toand from UE, not primarily connected other than via the high altitudeplatform antenna(s) with a large ground based communication network suchas the internet or a cellular network. Such antenna(s) can alsocommunicate with backhaul ground based stations (“BG stations”) whichare directly connected to a large ground based communication network andprovide “backhaul” known to those skilled in the art.

The UE may include transmitters or receivers or both. The aerialantennas can be phased arrays or conventional antennas or both.

FIG. 2 is an illustration of a small phased array (21). It has an arrayof small antenna elements (22), which are connected to either the inputof low noise amplifiers prior to digitization as a receiving system orto output amplifiers for transmission. Each antenna element is usedindependently and by controlling the precise time, or phase, of a signalbetween elements, a beam can be formed in a similar fashion as with aparabolic dish. The phased array may be designed so the antenna elementsare all planar, as shown in FIG. 2 where two or more layers (23) definethe electromagnetic performance. The phased array can also be a morecomplex shape, for example, “bowed” so that the outermost elements arepointing at an angle to the axis of the array.

The mechanism to form beams from a single receiving phased array isshown in one-dimension in FIG. 3, which shows beamforming on a singlearray. Phased-array beamforming is a well-established and understoodtechnology and this invention supports phased array antenna concepts. Byway of illustration a specific realisation is considered in which eachantenna element (36) is at a distance (37) from its neighbour of lessthan or equal to half the wavelength of the highest operating frequency;in the example shown in FIG. 3, which is designed to operate in the 2GHz bands (λ=15 cm), the spacing (37) is ˜7.5 cm. This enables the arrayto approximately detect the amplitude and phase of the receivedelectromagnetic signal. Each antenna element is connected to a low noiseamplifier. In order to form a beam for a flat array, the requirement isto have a linearly increasing signal delay across the width of thearray; this can be done in either the analogue or digital domain. Thediagram at the top of FIG. 3 shows the relative delays (32) on they-axis (30) used in producing the beam (35) where the distance acrossthe antenna is plotted on the x-axis (31). The signals from all theantenna elements suitably relatively delayed are then summed to form acomposite signal, which is a “beam.” The beam size is givenapproximately by λ/d where λ is the wavelength and d the diameter of thearray. In the case of a 2 GHz signal and a 1.5-metre diameter array, thebeam would normally be ˜5.7° wide. However, by appropriate antennaelement “weighting” this can be tailored to widen the beam. If requiredthis enables the beams to be varied to give approximately uniformcoverage on the ground as changes in the elevation of the array frompoints on the ground result in the beam being spread to a greater orlesser extent over the surface.

Phased arrays also have the benefit that, by using recent developmentsin digital technology, very wide bandwidths can be implemented. Thefrequency range of recent, planar antenna elements can be as high as 3:1from the lowest to the highest frequency supported. In such planarsystems multiple conducting or partially conducting layers are eachsituated in planes parallel to each other and at 90 degrees to the axisof the antenna.

Because all the signals from each antenna element are available for anyusage, it is practical to apply a different set of delays across thearray and sum the second set of signals and form a second beam. As alsoillustrated in FIG. 3: another beam (34) can be produced by a differentset of delays (33). This process can be repeated many times to form manydifferent beams concurrently using the array.

Forming many beams in the digital domain can be readily achieved, theonly requirement after digitization is additional processing resourcesand data bandwidth to communicate or further process all the beaminformation.

While it is possible to form a large number of beams with an individualphased array, the maximum number of “independent” beams that can carrydata unique from all other beams cannot exceed the total number ofantenna elements in the array. For example, if an array has 300independent antenna elements (separated by ˜λ/2 or greater) there can bea maximum of 300 independent beams; more beams than this can be formedbut these beams will not all be independent. In this instance thenon-independent beams will each transmit and receive the same (orsimilar) encoded information—these beams may still be utilised byappropriate resource sharing schemes or in other ways relevant to theinvention.

Phased arrays can form beams over a scan angle range up to approximately±60° from the axis normal to the plane of the array. This is due to thegeometrical limitation of the array where the illumination area of theelements is reduced as a cosine of the scan angle; also the sensitivityof the beam of the individual antenna elements is reduced due to theirbeing off the centre of the beam. The result is that the illuminationarea of a horizontal array is limited by the maximum scan angle toapproximately 60 km diameter with large single arrays for transmit andreceive, and this limit may be extended with more complex shaping of thearrays.

Referring to FIG. 6, the receiving array may consist of many planar dualpolarized receive elements (68) in a regular array (64). Twopolarisations are preferred for the inter-antenna beamforming techniquesdue to the need for precise amplitude and phase information; also toensure the best signal reception at the arbitrarily positioned UE. Eachpolarization is amplified, filtered and digitized over the receivebandwidth required. The antenna element electronics are convenientlymounted immediately behind the receive antenna element for low noisepickup, simpler assembly and to distribute the heat load over a largearea. The digitized signal for each polarization is transmitted to thesignal processing system for beamforming.

In one example, the array is 1.5-metres in diameter with antennaelements spaced at 7.5 cm. This results in approximately 315 antennaelements or 630 signal paths. This gives a service area of 60 kmdiameter broken into ˜160 patches (concepts for a modified array thatcan cover a wider area are discussed later in this document).

A position detection system (60), an orientation detection system (62)and a control and coefficient processor (61) interface with a signalprocessing system (63) which, in this preferred implementation, needs ahighly accurate clock system (66) which can be interfaced in turn to apositioning system (67).

The transmit array (65) is of a very similar design and size as thereceive array. It has many dual polarized transmit elements (69).Digitised signals are computed by the signal processing system for eachpolarization, transmitted to a digital-to-analogue converter, filtered,amplified, and passed to the output power amplifier for transmission. Aswith the receive array, the element electronics can be mounted behindthe transmit elements to distribute the heat load and minimize strayradiation.

Beamforming

The HAP-CELL system utilises beamforming across the multiple aerialantennas to generate narrow cooperative beams to the UE.

The system operates by the antennas, e.g. phased arrays on everyplatform in a “constellation” of multiple arrays, each forming one oftheir component signals onto a specific “patch”. The signal sent fromall the arrays to a specific patch carries essentially the sameinformation content (differences could include, e.g. noise fromquantisation and analogue effects), but has a phase delay across theconstellation of antennas, thereby forming a very narrow “synthesizedbeam” from the individual array beams.

The phase delay, or time delay for wide band signals, for the datasignal from each antenna to a UE is compensated accurately for thedifferent distances in phase space from individual antennas to the UE.The delay is calculated such that the signal to the UE from everyantenna arrives at the same time and is phase coherent at the UE. Signalamplitude from each of the aerial platforms is adjusted such thattypically all signals are normalised at the UE, but can be adjusted, forinstance to reduce side lobes. These adjustments are known as thecoefficients for each signal. A similar process is applied to the signalto each UE within a patch and combined to form the overall patch beamfor every aerial antenna. These beam forming instructions can either becalculated on the ground in a processing centre and transmitted as anencoded representation of the patch beam to each aerial antenna or usedat the platform to form the patch beams.

For signals transmitted from the UE to the constellation of aerialantennas the processing system similarly applies phase or time delays tothe patch beam from every aerial antenna in the constellation and thensums them to form a coherent receive beam on a UE. This combined signalis used to communicate with the wider cellular network. Typically thisprocessing will be carried out at the ground processing centre whichreceives an encoded representation of the patch beams received at theaerial antenna.

The synthesized beams are computed to become “user beams” which trackspecific UEs. This is illustrated in FIG. 4, which shows beam formationin the service area, by a constellation of antennas labelled HAP₁, HAP₂to HAP_(m). The antenna on HAP1 is shown producing three beams (40,42,and 44), which are directed at three patches (41, 43, and 45). HAP₂ andHAP_(m) are shown producing similar beams.

The size of the synthesized beam is much smaller: ˜λ/D where D is themaximum diameter of the constellation of antennas. If, for example, theantennas are situated within a circle of diameter, D=10 km, at thecentre of a service area of 60 km diameter, then for a 2 GHz signal thebeam is only 0.1 arc minutes wide; which results in a beam diameter ofonly 60 cm diameter at ground level directly underneath the antennaconstellation or less than 3 metres diameter at the edge of the servicearea. The small size of the area these user beams interact with is shownby the areas (46).

The minimum size of the area on the ground, the “resolution area,” whichan independent beam from a single aerial antenna could interact with,varies with its position relative to the aerial antenna. The “maximumbeam data rate” (MBDR) that can be transferred to or from a singleantenna within a beam is given by the number of bits per second perHertz bandwidth, multiplied by the bandwidth available. The maximumnumber of bits per second per Hertz is limited by the signal to noiseratio of the signal, as is well known to those skilled in the art.

The beam sizes can be adjusted to be larger than the minimum beam sizefor a single antenna, so that area illuminated by each beam may betailored to the requirements of the operational environment of thesystem.

If all the aerial antennas are relatively close together compared to thediameter of the service area, these resolution areas will be comparablein size from one antenna to another. If the aerial antennas are farapart, the “resolution areas” from different antennas will be verydifferent in size. There is a limit to the amount of data that can betransferred within one resolution area given by the number of antennasin the constellation multiplied by the MBDR if the resolution area sizesfrom each of the antennas are similar. The available bandwidth can besplit into multiple blocks of resources, e.g. frequency bands, timeslots and codes, thereby increasing the number of UEs that can besupported although with a lower data rate available to each UE. Otherradio resource sharing techniques can be used. There cannot be more datapresent in the user beams than is available in the antenna beams.

In the HAP-CELL system, the constellation of aerial antennas effectivelyoperates just as would a single antenna having a dimension that is from1 to 30 kilometres, preferably from 5 to 20 kilometres. Thus, verynarrow beams can be generated.

Weightings on the antenna elements can be varied to control ground basedpatch sizes based on an optimization function reflecting populationdensity or data rate density, taking into account the orientation andattitude of the antenna platform(s). In this manner if the centre of theconstellation is over a large city but at the edge of the service areathere is a low population density, beams to and from the constellationmay involve only a small fraction of the antenna elements of each arraythereby saving power.

Platforms Supporting Antennas

Platforms can be implemented as:

(i) Aircraft that are powered using either solar energy or hydrogen orhydrocarbon fuel to carry the communications equipment at approximately20 km. The aircraft carry the equipment for communicating with UEs andwith the BG stations. Also, they carry the signal processing systems,precise clock and timing units and control computers.

(ii) Free flying aerostats powered by solar cells or other technologies.The aerostats carry the equipment for communicating with UEs and withthe BG stations. Also, they carry the signal processing systems, preciseclock and timing units and control computers.

(iii) Tethered aerostats powered by hydrogen conveyed along the tether,or supplied with electrical power via the tether or supplied by solarcells situated on or connected to the aerostat platforms. A tetheredaerostat supporting one or more tethers can carry a number of platformsat a number of different altitudes with each platform in turn supportedby the tether(s). Each platform may also receive additional support fromits own aerostat. The tethered platform system carries the equipment forcommunicating with UEs and with the BG stations, and they may carry thesignal processing systems, precise clock and timing units and controlcomputers or this may be ground based. FIG. 9 shows the layout of such asystem.

In the case shown there are tethered aerostats (90, 91) connected bytethers either directly to the ground (93) or indirectly (92). Someaerostats (91) are connected indirectly, and some directly (90) to theground. In the case shown, the antennas (94) are wholly contained insidethe envelope of the aerostats. They may be partially contained or notcontained at all. UE (96) is communicated to by beams (95) from theaerial antennas (94) in a co-operative manner. At least two antennascommunicate with each UE.

(iv) Ground-based antennas based on very high towers or buildings wherethere is significant movement of the antenna of at least 1/10 of thewavelength of the carrier signal.

(v) Conventional commercial aircraft used for passenger transportsupporting additional intermittent aerial antenna capability.

(vi) Space-based satellites.

(vii) Hybrid air vehicles.

The system may consist of one or several types of platform describedabove.

Platform Communications with UE

The platforms are normally all equipped with at least two phased arraysof equivalent size and number of elements, a transmit array and areceive array, to enable the system to have concurrent transmission andreception for any waveform and multiplexing technique that operates atthe selected frequency allocation and bandwidth. It is possible to use asingle array, but the electronics required is of greater complexity andweight, and may only support time division multiplexing and not the moreusual frequency division multiplexing. The arrays form beams that dividethe service area into a number of patches. The patches are treated as“cells” by the cellular telephone network.

The UE may be ground based or could be on a manned or unmanned aircraftat lower altitude than the aerial antennas. The UE could also be carriedon some form of transportation technology including but not limited totrains, motor vehicles and shipping.

Backhaul Communications

The HAP-CELL system can provide a “transparent” link between thecellular network and the individual users' devices in a similar fashionas conventional ground based mast based systems. This providescompatibility with the existing cellular network.

The system allows for the possibility of a substantial amount of datacommunicated between the platforms and the UEs. Thus there has to be atleast the same amount of user data communicated through the backhaulsystem to and from the platform and processing system. There are thefollowing options for transmitting the data from and receiving it to theplatforms via the following communication links:

-   -   1. Use capacity on the phased arrays used for communication to        UE on each platform    -   2. Use alternative, high capacity links on alternative phased        arrays    -   3. Use single beam point-to-point high capacity links    -   4. Use free-space optical links to BG stations.    -   5. Use free-space optical links between platforms, so that a        platform in a less well-developed area can communicate by laser        to a satellite or aircraft that has a microwave downlink to BG        stations. This can be via a series of repeater platforms with        redundancy.

Both polarisations could be used independently on the backhaul link,potentially halving the number of BG stations required.

The embodiment described below will use implementation 1 above and shareresources on the large arrays to provide both the backhaulcommunications and the user links.

Much of the technology used in the present invention is used in thetelecommunications industry and develops techniques used in radioastronomy for beamforming and beam shaping. The use of one-dimensionalphased arrays, the interface specifications, the data encodingtechniques, the use of signal processing etc. are all widely used by theexisting cellular telecommunication systems. The present inventionintegration results in a very high performance system that interfacescompatibly into most existing cellular telephone network technology.

Processing System

The HAPS-CELL system is managed by a processing system, which may be adistributed system or, as shown in the figures, FIG. 1 shows aprocessing centre (1), which is normally ground based, saving weight andpower on the aerial platforms. The processing system interfaces to thecellular telephone network (2), and it provides direct control of thesignals being used by the platforms to communicate with the UEs.

The processing system may be physically distributed between a processingcentre, processing co-located with the aerial antennas and/or backhaulground stations, and processing services provided by third-party (knownas “cloud”) providers.

The processing system provides the interface to the cellular networkthrough a defined interface to the cellular network.

The processing system computes for the aerial antennas:

(i) The beamforming coefficients required for the signals received fromthe UE and BG stations both for antennas and if these are phased arrays,normally but not exclusively the coefficients for the antenna elements.

(ii) The phases and amplitudes for the signals to be transmitted to UEand BG stations.

(iii) All algorithms to implement operational aspects such as positionaldetermination of platforms and user equipment.

For BG stations the processing system can compute and provide

(i) The coefficients for the signals to be transmitted by the BGstations to the aerial antennas.

(ii) The coefficients for the signals received from the BG stationantennas and if need be the antenna elements if the BG stations areusing phased array antennas.

The BG stations can be linked directly to a processing centre viahigh-speed connections such as fibre optic data links or directmicrowave links.

The signals at the platform are complex in that they define all thecharacteristics to enable the constellation of platform phased arrays tobeamform precisely onto individual users.

All these signal processing and beamforming calculations are performedin the processing system. The processing system may comprise at leastone processing centre with some processing required on each platform.Such processing centres are ideally located at ground-level, forsimplicity. Preferably however, ground level processing dominates theoverall signal processing capability, consuming over 70 percent,preferably over 90 percent of the signal processing electronicselectrical power requirements.

The processing system also determines how the system presents itself tothe cellular network, including providing the required interface toenable efficient resource allocation.

The processing system may be capable of a further range of enablingfunctions, as will now be illustrated. The processing system may becapable of determining when the formation of a DF-Cell is required topermit up to the maximum resource allocation to a given piece of userequipment. The processing system will support all resource allocationmethods required by the cellular network including, but not limited to,frequency and time multiplexing. The processing system will alsodetermine the frequencies that will be used by each platform. This canbe up to the full bandwidth of the frequency allocations or restrictingthe bands for specific network or mobile phone operators using eitheroverlaid systems according to the present invention or a mixture ofground based antennas and the present system. It would also supportco-operative use of multiple operators, assuming suitable agreements canbe reached.

The system can also use time division multiplexing or other radioresource sharing techniques.

Programmable signal processing components, Field Programmable GateArrays, FPGAs, are now of a power and capability suitable for thissystem. Such devices are now available that can perform this task, e.g.the Kintex(http://www.xilinx.com/products/silicon-devices/fpga/kintex-ultrascale.html)family of devices from Xilinx, which feature up to 8 Tera MACs(Tera=10¹²; MAC=Multiply Accumulate, the basic processing operation indigital signal processing) processing capability and 64×16 Gb/scommunication channels using modest power, typically under forty watts.

The signal processing system uses information transmitted from theprocessing centre to form required beams on the UEs and (if required) onthe BG stations. The data in the beams that are formed is retransmittedto users, BG stations or used by the control processors on the aircraft.

As discussed, processing on the platforms is preferably minimised,however there may be at least some processing carried out there whichcan include:

-   -   Reconstruct the coefficients used by the signal processors to        form the required beams;    -   Use information from the position and orientation systems as        part of the beamforming process;    -   Monitor, control and report the status of the aircraft payload        systems.

The processing capabilities required are of the order of a conventionalPC server, but as a specialist implementation requires less power.

Accurate time determination at the moving aerials is essential to theprecise reception and beamforming of the signals.

It has been found that a suitable clock generation uses a GNSS systemfor long-term (greater than ten's of seconds) accuracy and an oventemperature stabilized crystal oscillator for short-term accuracy. Thiscombination will give the phase precision required for both localaircraft beamforming and beamforming between aircraft. The requirementis to have phase stability for the analogue to digital converters, ADCs,and digital to analogue converters, DACs, to have precise sampling atall times.

Backhaul Ground Stations (BG Stations)

As discussed, the cooperative aerial beamforming system involves theprovision of one or more BG stations. The BG stations can provide thecommunication links to and from the platforms and the processing centre.Each BG station should be able to communicate independently with as manyplatforms in line of sight as possible, to maximize the data ratecapabilities of the platforms.

Typically, there are therefore at least as many beams formed at each BGstation as platforms visible from the individual BG stations. Usingphased arrays as the communication system at the BG stations willprovide this facility. The design of these phased arrays can be similarto those on the platforms.

BG stations provide the high-speed data links between the aircraft andthe HAP-CELL processing centre. To reduce the number of BG stations andtheir associated costs, it is useful for the BG stations to havemulti-beaming capability so that they can each communicate with eachaerial antenna independently when there is a constellation of multipleantennas, to provide the high data rates required for the network. Bythis means the data rate to or from each BG station can be increased bya factor equal to the number of aircraft being communicated with overthat which would be possible with a single aircraft.

An implementation using phased arrays similar to the systems used on theaircraft is illustrated in FIG. 7. As with the aircraft phased arraysthere are separate transmit (75) and receive (74) arrays.

The receive array (74) has a large number of elements (78) which providesignals to the receiver processing system (72). The transmit array (75)has a large number of elements (79) which receive signals from thetransmitter processing system (73). Both receiver and transmitterprocessing systems interface (71) with the HAPS-CELL processing system(70). They also can require input from a clock system (76), which inturn receives input from a positioning system (77). BG stations areseparated far enough apart for beams from the individual aircraft arraysto resolve them independently with different array beams. This is toprovide a sufficient aggregate data rate to every aircraft.

In the example shown, BG stations are under the direct control of theprocessing system; the processing system determines the amplitude andphase for every array element.

In certain locations where the availability of BG stations is low, itmay be advantageous to link one aircraft with another more suitablylocated over BG stations by laser or free space optical devices. Thesehave been developed in recent years and allow high data ratecommunication (greater than 1 Giga bit per second) with modest (under100 W) power consumption and can be of modest weight of less than 25 kgbut able to communicate in the stratosphere at distances of at least 60km, and more preferably of 250 km and on occasion of 500 km or more.With such an arrangement it is possible for one or more aerial antennasto be linked to BG stations many hundreds if not thousands of kilometresdistant by utilizing laser links between additional aircraft.

Aircraft Based Communication System

For communicating with the UEs the aircraft are fitted with large phasedarrays and associated signal processing and control systems, asillustrated in FIG. 6.

There are two phased arrays: one for receive (64) and the other fortransmit (65). This is to ensure that there is full separation betweenthe two paths such that both systems can operate using frequencydivision duplex, FDD, systems; these are the most popular cellular phonecommunication links. Two arrays can also support the alternative timedivision duplex, TDD, systems without the complexity of sharing an arrayfor both transmit and receive.

As discussed above, these arrays both have many individual receive ortransmit elements (68, 69); the array signals are combined in the signalprocessing system (63) to produce the required beams.

Finding the Position and Tracking Users During a Connection

The system can keep track of UEs in a similar fashion to a conventionalground based network. The UE needs to be kept within the cooperativebeam when a call or data transfer is in progress.

When using Inter-Aerial Antenna beamforming the beam on the UE could bevery focused, of e.g. approximately 1 metre diameter. There are then twofurther functions required:

-   -   To sufficiently identify the required antenna weightings to        allow such a focused beam to establish a connection;    -   To adjust these weightings appropriately during the connection        to allow for the movement of the aerial antennas and the UE.

It has been discovered that by using the arrays within the constellationto “focus” on the UE by using progressively more and sometimes differentantennas as part of the beamforming process such a process can beachieved. By optimizing the beamformed location for signal strengthprior to including more aircraft, then the relevant antenna weightingscan be optimized. The focusing process can be speeded up substantiallyby the UE reporting its GNSS position, if that function is available.

During a connection the UE can move out of the beam. Narrow bandwidthsecondary beam(s) can be used to rapidly sample in a pattern around theuser's position. Increased signal strength in a particular direction orarea can then be used to modify antenna weightings and beam position anddirection.

Thus, in the HAP-CELL system, normally the first cooperative beam isgenerated at a first point in time, and at a second point in time,carrying out a second beamforming operation to ensure that thecooperative beam is directed to the position of the moving user antenna.

Beam Shaping and Sidelobe Minimization

The requirements of beam precision for cellular networks are quitestringent, particularly for energy spillover at national boundaries. Agreat benefit of using phased array techniques rather than fixed dishesis the ability to modify the beams electronically.

Setting the appropriate amplitude and phase delay on the antennaelements forms and steers beams. When there are many antenna elements,this gives flexibility in shaping the beam to the specific requirementsby trading off sensitivity and beam control. The result is that thepatches can be well defined and the edges of the service area can becontrolled closely to minimize sidelobes or other artefacts to affectneighbouring areas.

FIG. 10 illustrates an example of how beams from one or more aerialantenna(s) can be modified to give good coverage up to a nationalboundary but minimize energy spillover into an adjacent country.

In diagram 130 in FIG. 10, patches of coverage beams from individualantennas or multiple antennas follow a regular grid arrangement wherethe position of the grid elements is given on the x-axis (133), in thiscase East-West, by numerals and on the y-axis (132), in this caseNorth-South, by letters. For example the element 136 can be referred toas having location G7. An irregular national border is shown (135).

Shaded squares illustrate to where energy is being transmitted by theaerial antenna system. It can be seen that to ensure low spillover ofenergy there is an area next to the border where little energy istransmitted, for example in patches A6, B7, C7, D5, E5, F8 and so forth.

Diagram 131 in FIG. 10 shows the same area, with the same y-axis (132)and a comparable x-axis (134) but with modification of the antennaelement and antenna phasing—and if need be amplitude, to move thepatches to the left or right to more closely follow the national border.For example cell G7 (136) has moved, along with its row (G1 to G5) in aneasterly direction so it has become located at a new position (137). Theuncovered area closer to the national border has been significantlyreduced.

The synthesized beams formed using Inter-Antenna beamforming can besimilarly controlled, trading sensitivity for beam-shape to minimizeartefacts and actively control beamsize.

Data Rates

The data rate available depends upon the bandwidth available from theband that is in use. For this embodiment, it is assumed that the band isLTE Band 1 (other frequencies are also available):

Uplink: 1920 MHz to 1980 MHz 60 MHz bandwidth Downlink: 2110 MHz to 2170MHz 60 MHz bandwidth

In certain embodiments the links to individual UEs will only use thebandwidth required for the function being used, hence the bandwidth canbe sub-divided to service as many users as possible.

The data rates through an example HAP-CELL system are shown in Table 1.As can be seen, this is using Band 1 frequencies and 50 aircraft in afleet. The data rates per link are dependent upon the signal to noiseratio of the link; hence there is an expectation of higher data rates inthe same bandwidths for the backhaul links than to the UEs. This isbecause the connection to the backhaul can be much better managed due tothe fixed, outdoor nature of the equipment and the potential for usinghigher transmission power and larger antennas than for mobile UE.

As can be seen, the maximum data rate to the UE is very high, assumingthe use of clear, high SNR connections. As with all cellular networks,the data rate will be adjusted for the actual link performance.

There is a very strong trade-off of the number of BG stations and thepower that can be used for each link. It is worth noting that thedominant data communications will be between the network and the user,with typically a lower data rate on average on the return path. Thismeans that a higher power can be used from the ground stations to theaircraft for a higher number of bits per Hertz for a better spectralefficiency; also, a higher power for transmission from the aircraft thanis used by the user for enhanced data rate on that link.

Use of 28/31 GHz Bands

There are frequency bands at 28 GHz and 31 GHz allocated by theInternational Telecommunications Union to HAP downlink and uplinkcommunications as follows:

Downlink: 27.5 GHz to 28.35 GHz 850 MHz bandwidth Uplink: 31.0 GHz to31.3 GHz  300 MHz bandwidth

These provide considerably more bandwidth than the 2 GHz frequenciescommonly used for mobile networks, but are harder to implement withconventional electronics—particularly as a phased array.

TABLE 1 Example HAP-CELL system, 50 aircraft, 1.5 m 2 GHz single arrays(values used for indicative sizing of the system) System Value CommentsNo. of Aircraft 10 to 50 Aircraft in a single fleet No. of BG stations157-416 This depends upon encoding and number of polarisations onbackhaul links. Bandwidth 60 MHz LTE Band 1: Chosen band forillustration purposes Wavelength, λ 15 cm ~2 GHz Aircraft height 20 kmLower stratosphere and well above commercial airspace Service areadiameter 60 km Within max. scan angle of aircraft phased arrays allowingfor pitch and yaw of aircraft Platform mounted phased array: Diameter1.5 m Selected to fit on the aircraft with good performance Number ofantenna elements 315 ~1.5²*π/(4*(0.075)²). (Area of array)/(area ofantenna element) Polarisations  2 Dual polarization for beamforming andhigh reliability for user links. Max. antenna scan angle 60° Physicallimitation, 20tan(60°) = 34.6 km, defines Service area No. of arraybeams formed ~160  50% × number of antenna elements: The number ofpatches is restricted for good definition of the edges. Patch size 4.7km × 4.7 km Defined by the size of the arrays Backhaul data links:Implementation Phased Uses additional virtual patches on the aircraftphased array beams arrays Polarisations  2 Dual polarization, forbeamforming performance. In principle could use separate polarisationsfor data - but not considered here. Modulation 256-QAM 8-bit/symbol.Data rate per link (max) 480 Mb/s 8-bit/s/Hz * 1 polarisations Data rateper link (min) 360 Mb/s 6-bit/s/Hz (64-QAM) * 1-pol Data rate per BGstation 18 Gb/s Direct communication with 50 aircraft (in thisexample) - 1 Polarisation User data links: Patches 160 For a 60 km dia.service area with 1.5 km patches Polarisations Identical Identicalinformation to avoid phone orientation issues Modulation, max Up to64-QAM 6-bits/symbol. This is the fastest modulation on very good linksModulation, average 2-bit/symbol The average data capacity per link.Data rate max for 1 user 360 Mb/s The absolute max data rate with fullBW and 64-QAM Data rate per aircraft (typ.) 19.2 Gb/s 120 Mb/s perpatch * 160 patches System Data rates: Data rate per patch, max 6 Gb/s120 Mb/s per plane, 50 planes Data rate over Service area, 960 Gb/sAssuming 50 planes in fleet in line of sight max

Power Requirements for Aircraft Payload

The payload power usage on the aircraft considered is for thecommunications arrays, the digital processing systems on board and thecontrol and positioning systems. Keeping the aircraft payload powerrequirements low is important for the limited power availability ineither the solar powered aircraft or hydrogen-powered aircraft operatingat high altitude.

For the phased array receivers and transmitters the power will scale asthe number of antenna elements. Performing as much processing as ispractical in the ground based processing facility minimizes theprocessing requirements at the aircraft. The power for the large numberof digital interfaces will dominate the processing power.

Estimates for power consumption are shown in Table 2. This is an examplecalculated for an aircraft incorporating two 1.5 m diameter phasedarrays for transmit and receive. Each array has 315 dual polarizationantenna elements; each array therefore has 630 signal channels. Thepower requirements are for ˜1.6 kW with these arrays.

The elements of the processing system located on the platform areimplemented using standard components and as such will benefit over timefrom the improvements in processing available per unit of powerconsumed.

This would scale almost linearly with the number of elements or with thediameter of the arrays squared. Hence 3-m diameter arrays would beapproximately four times this power requirement.

TABLE 1 Estimated power requirements for airplane with 2 × 1.5 m 2 GHzarrays Power Power each total Subsystem (W) Number (W) Comments Receivearray: LNA & gain chain 0.5 630 315 Digitisation & 0.2 630 130communications Power losses 45 10% power distribu- tion losses Transmitarray: DAC & 0.2 630 130 communication Power amplifier 0.5 630 315Assuming 250 mW RF power per polarization Tx, 50% efficiency Powerlosses 45 10% power distribu- tion Signal processing: Processing 200 10FPGA's at 20 watts (processing) each Signal transport 0.1 630 65Inter-FPGA links Control, clocks, orientation: Estimate 400 Substantialprocessing resources Total 1635

Effect of Aircraft Based Communications on Mobile Users

Communication links between aerial antennas and BG stations willnormally be at above 30 degrees elevation resulting in a consistentsignal for a given location. For UE the signals to and from the aerialantenna will often be passing through roofs of buildings, which willresult in significant losses. However, in large systems, with manyaircraft over adjacent, or overlapping service areas, then there is ahigh likelihood of signals coming in obliquely through windows andwalls, which are typically more transparent to the signals.

The aircraft are up to 35 km away and have a round trip link of morethan 70 km; the processing will have some buffering delays. The delayswill not add up to more than a few milliseconds which is well withincurrent mobile network specifications of <30 ms or proposed 5 Gspecifications of <5 ms.

Multiple Service Areas

The HAP-CELL system is intended for use over large areas. For denselypopulated areas, e.g. major cities, there may need to be multiple fleetsof aircraft serving multiple service areas. The system readily scales inthis fashion and economies of infrastructure and additionalcommunication capabilities become available. A multiple system isillustrated in FIG. 8. There are three fleets of aircraft (85, 86, 87)identified. These form beams on patches either in their uniqueilluminated area, e.g. (88) or overlapping areas, e.g. (89). Thecellular network and Internet (81) interfaces with one or moreprocessing centres (82), which are linked by fibre optic cables or bymicrowave (83) to BG stations (84 or 841). Each service area (810, 811,812) is approximately 60 km in diameter. As can be seen, the serviceareas can overlap which provides higher total data rate for users. Thereis also the benefit of improved coverage, for example, if a user isshielded from a fleet of aircraft by being on the “other side” of abuilding, then there is likely to be coverage from an adjacent fleet.

Due to the user beam from a fleet of aircraft being “private” to anindividual user there is no significant interference from adjacentfleets, or beams from adjacent fleets that are spatially separated.

There will be a significant saving in infrastructure. BG stations (841)can service more than one fleet of aircraft if they are suitablypositioned. The BG stations form beams to each aircraft within a fleet,consequently, provided the fleets are within range then a BG station canservice all the fleets within 30 km to 35 km.

The design of an area's coverage should consider how a number ofaircraft, e.g. 50-100, should be deployed in fleets to have maximumbenefit. There may be more, smaller fleets or fewer large ones withappropriate degrees of service area overlap. The details will dependupon the population density and other factors, but the HAP-CELL systemcan allow these trade-offs to be made.

Improving the backhaul data provision according to the present inventionsupports the benefits described below:

Summary of Benefits of the Aerial Inter-Antenna Beamforming System

Wide coverage area: The horizon for an antenna on a platform at 20 kmaltitude is at approximately 500 km radius. The elevation of such aninstrument from any particular location on the ground is defined as theangle the instrument is above the horizontal at that point. For theplatform to be above 5 degrees elevation, any location on the groundwill be within a circle of radius 200 km centred directly below theplatform. For elevations greater than 30 degrees the location must bewithin circle of radius 35 km centred below the platform. The latterconstraint is appropriate for communications between the ground and aplatform carrying only phased arrays situated in a horizontal plane. Theformer constraint may be appropriate for more complex array geometriesbut signal strength will become a limiting factor at distances over 100km which is discussed later.

Low installation cost: Use of platforms reduces the need for groundinstallations that are both time-consuming to install and expensive torun. Existing ground installations can be used in conjunction with thesystem to greatly increase capacity and coverage.

High data rate links: The traditional operation of a mobile networkdivides the network into a set of “cells.” Multiple UEs within a cellmust share the available resources (signal bandwidth and communicationpower), which determine the maximum data rate to a user either by radioresource sharing techniques, for example, but not exclusively, sharingbandwidth or time multiplexing. A key element of HAP-CELL is thatinter-antenna beamforming is used to create a DF-Cell centred on aspecific device. This permits all the resources which can be madeavailable by the implemented protocol to be used by a single device.Resource sharing as in standard implementations, is also supported bythe invention.

Focused RF power at the user: Due to Inter-Antenna beamforming the powerat the precise user location is increased. This minimizes the powerusage on the platform and improves link quality. This is described indetail in Tables 2 and 3.

Scalable capability: The number of users and data rate can be increasedeasily and quickly—without normally the need for additional ground basedinfrastructure—by adding more platforms in the same area. The additionof extra BG stations can normally be avoided unless very large capacityincreases over the previous infrastructure are needed. This feature, initself, provides substantial resilience in the system. For example,losing one platform out of ten similar platforms, due to an equipmentfault or maintenance or temporarily being unavailable due to flightpatterns, would reduce the capacity of the system by 10%, but still givecomplete coverage within the service area. Similarly, losing one groundstation out of a hundred would also only lose 1% of the communicationdata rate capability. This is significantly better than the loss of astandard mobile phone cell mast where all users within the cells itcontrols will lose the signal.

Coverage area can be accurately tailored: Phased array and beamformingtechnology enables the coverage area to be more accurately controlledthan with ground-based systems. This is important for operation close tocountry borders.

For reliable communication, the beamforming technology needs to managethe effects of reflections such as from walls; or diffraction effectssuch as from the edges of intervening objects, such as the roofs ofbuildings, if the UE is ground based. Ideally the antennas on many ofthe platforms are in line-of-sight or close to it from the UE.

TABLE 3 Glossary of terms used in this document ADC Analogue to digitalconverter. Within the HAP-CELL systems converts the analogue RF signalto digital data stream for signal processing. Algorithm A process orcode by which the power levels at a particular UE can be set. This mightbe to optimise the powers to antenna elements to ensure a minimum powerlevel for all UE's or to ensure that given UE's had a higher powerlevel. Antenna A phased array or conventional antenna. Antenna elementAn individual transmitting or receiving antenna within a phased array.Each has an individual electronic system for linking to a signalprocessing system. Antenna weightings Typically complex numbers that areused within the signal processing chain to adjust the amplitude andphase of the signals to and from individual antenna elements to form thedesired beams from an antenna or constellation of antennas. Backhaul Thedata communication links from the aerial platforms to the ground andcommunications ultimately to the HAP-CELL processing centre. BeamDirectional signal transmission or reception from an antenna BeamformingBeamforming is a signal processing technique used for multiple antennasor in the case of phased arrays, antenna elements, to give directionalsignal transmission or reception. This is achieved by combining thesignals transmitted or received so that at particular angles theyexperience constructive interference while others experience destructiveinterference. Beamwidth The angular beamwidth, as understood bypractitioners skilled in the art, depends upon the ratio of thewavelength of the radiation used in said communications system dividedby the separation between pairs of aerial antennas; for the conditionsenvisaged for this invention may be designed to be a wavelength of 15centimetres and an aerial antenna separation of approximately 10kilometres results in a beamwidth of less than 50 micro radians and beamsize on the ground of less than 2 metres Beamforming Typically, theseare complex numbers that are used within the signal coefficientsprocessing chain to adjust the amplitude and phase of the signals to andfrom individual antenna elements to form the desired beams from an arrayor constellation of arrays. BG stations Backhaul ground stations. Theground based radio links to each of the platforms. Cell The logicalfunctionality provided within an area on the earth's surface suppliedwith radio service. Each of these cells is assigned with multiplefrequencies. Constellation A number of antennas supported by HAPsoperating cooperatively over the same service area to providecommunications to many UEs. Conventional Antenna An antenna which is nota phased array Cooperative beam A highly directional signal transmissionor reception formed by coherently aligning beams from multiple antennasmounted on aerial platforms. Correlating Correlating is a mechanism tocross-multiply the signals to or from pairs of antenna elements, this isa fundamental part of interferometry to form the Fourier transform ofthe incoming or outgoing signals. DAC Digital to analogue converter.Within the HAP-CELL system converts a digital data stream into ananalogue RF signal for amplification and transmission via an antennaelement. DBF Digital beam-forming Femtocell The area, normally on theground, which is intersected by a beam carrying information to and froma piece of UE and at least three aerial antennas involved ininter-antenna cooperative beam forming. Dynamic femtocell (DF Afemtocell that is moved by changing antenna weights. Cell) Fleet Fleetof platforms supporting a constellation of antennas. HAP High AltitudePlatform. This is the vehicle that carries the communications equipment.It can e.g. be an unmanned aircraft, tethered balloon or untetheredballoon. HAP-CELL High altitude platform cellular system, which refersto an example of an implementation using HAPs to provide cellularcommunications. HAP-CELL Processing A facility associated with one ormore HAP-CELL systems to control the centre communications to and fromBG Stations, HAPs, UEs and the cellular network. Macrocells A cell in amobile phone network that provides radio coverage served by a high powercellular base station. MBDR Maximum Beam Data Rate from a single antennain a independent beam MBH Multiple beam horn (antennas) Microcell Amicrocell is a cell in a mobile phone network served by a low powercellular base station, covering a limited area such as a mall, a hotel,or a transportation hub. A microcell uses power control to limit theradius of its coverage area. Patch The patch is a specific area,normally on the ground, which can be illuminated by every antenna in theconstellation with an independent beam. Payload The equipment carried ona Platform. Phased Array A type of antenna consisting of many smallantenna elements, which are controlled electronically to form one ormore Phased Array Beams. Phased arrays can be used on the HAPs or BGstations Phased Array Beam The electromagnetic beam formed by a phasedarray. Phased array beams from a HAP illuminates a patch. Platform Theplatform that carries the payload - an aircraft, tethered aerostat orfree flying aerostat. Service Area The area of ground over whichcommunications coverage is provided by one or more HAP-CELL aircraft. Aservice area is split into many patches. Spread Spectrum A technique inwhich a telecommunication signal is transmitted on a Technologiesbandwidth considerably larger than the frequency content of the originalinformation. Synthesised Beam The beam formed by beamforming HAPs in aconstellation. The beam is small and illuminates a “dynamic femtocell.”Transmitting data Data can be transmitted over an RF link such as theaerial antennas. Can also refer to communicating data within a systemover local links such as fibres or wires. UE See User Equipment. UserEquipment The equipment used by an individual user, typically but notexclusively a mobile phone, tablet, or computer. Abbreviated to UE. UserBeam A synthesised beam that tracks specific user equipment WeightingsSee Antenna weightings

1. A process for cooperative aerial inter-antenna beamforming forcommunication between (a) multiple moving platforms, each platformhaving an aerial antenna mounted thereon, such that the aerial antennashave variable positions and orientation over time, and (b) at least twoground based antennas; the process involving transmitting data relatingto the positions of the aerial antennas to a processing system, theprocessing system calculating and transmitting beamforming instructionsto the ground based antennas, the ground based antennas therebytransmitting or receiving respective component signals for each aerialantenna, the component signals for each aerial antenna received ortransmitted by the ground based antennas having essentially the sameinformation content but differing in their phase and usually amplitude,so as to form a cooperative beam from the cooperative sum of the signalsbetween the ground based antennas and the aerial antennas.
 2. Anapparatus for providing a communication network, for communicationbetween (a) multiple moving platforms, each platform having an aerialantenna mounted thereon, such that the aerial antennas have a variableposition and orientation over time, and (b) at least two ground basedantennas; the network involving a processing system that calculates andtransmits beamforming instructions to the ground based antennas, theground based antennas thereby transmit or receive respective componentsignals for each aerial antenna, the component signals for each aerialantenna having essentially the same information content but differing intheir phase and usually amplitude, thereby forming a cooperative beamfrom a cooperative sum of the signals between the ground based antennasand the aerial antennas.
 3. The process according to claim 1, whereinthere are at least three aerial antennas.
 4. The process according toclaim 1, wherein use of two orthogonal polarisations for each transmitor receive beam for backhaul communications between the ground stationsand the aerial antennas is employed to provide two separate data streamswhich increases the data transfer rate on backhaul links by up to doublethat of a conventional link.
 5. The process according to claim 1,wherein the positional and orientation data is transmitted by the aerialantennas to at least one ground based station.
 6. The process accordingto claim 1, wherein the processing system comprises a ground basedprocessing centre.
 7. The process according to claim 4, wherein groundlevel processing dominates the overall signal processing capability,consuming over 70 percent of signal processing electronics powerrequirements.
 8. The process according to claim 1, wherein at least oneaerial antenna is at an elevated location of at least 10,000 m in thestratosphere.
 9. The process according to claim 1, wherein at least oneof the aerial antennas are phased array antennas.
 10. The processaccording to claim 1, wherein the platforms comprise unmanned solarpowered aircraft, airships or hybrid air vehicles.
 11. The processaccording to claim 1, wherein the platforms comprise unmanned hydrogenpowered aircraft.
 12. The process according to claim 1, wherein theplatforms comprise tethered aerostats.
 13. The process according toclaim 1, wherein the platforms comprise free-flying aerostats.
 14. Theprocess according to claim 1, wherein the platforms comprisehydrocarbon-fueled aircraft.
 15. The process according to claim 1,wherein the platforms comprise satellites.
 16. The process according toclaim 1, wherein at least some of the platforms use different antennasfor transmission or reception.
 17. The process according to claim 1,wherein data rates to and/or from a user equipment antenna exceed 10Mbps.
 18. The process according to claim 1, wherein the use of lasers orfree space optical devices is employed to provide a communication linkof backhaul data between aerial antennas involved in cooperative interantenna beamforming.
 19. A process or apparatus according to claim 18,wherein the platforms comprise a control system to adjust the positionof the platform so that it does not break line-of-sight of the laser orfree space optics communication stream.
 20. A method of receiving and/ortransmitting data, applications and/or content to an antenna on userequipment, the method utilising the apparatus according to claim
 2. 21.A computer program comprising computer implementable instructions whichwhen implemented on a computer causes the computer to perform theprocess according to claim
 1. 22. A computer program product comprisinga computer program according to claim 21.